1. Field of the Invention
The present invention relates to an acrylic elastomer composition and more particularly to an acrylic elastomer composition effectively applicable as a vulcanization molding material for seal members or hose members to be used at contact sites with a metallic member, oil, etc.
2. Description of Related Art
Automobile seal members or hose members require a metal corrosion resistance, an oil resistance, compression set characteristics, etc. and these requirements are more strict on more diversified year by year. Thus, special rubber materials are in demand. But, conventional acrylic elastomer compositions actually fail to satisfy all of these requirements.
For example, active chloride group-containing acrylic elastomers compounded with a triazine compound and a metal salt of dithiocarbamic acid have been used as rubber materials having distinguished compression set characteristics, but are not satisfactory for metal corrosion resistance-requiring uses. On the other hand, epoxy group-containing acrylic elastomers have been used in such metal corrosion resistance-requiring uses, but have not satisfied the strict metal corrosion resistance now in demand yet.
Known rubber materials containing no such active halide groups include a terpolymer of ethylene-butenedionic acid monoester-acrylic acid monoester (JP-A-50-45031), where only a terpolymer of ethylene-monomethyl maleate-methyl acrylate is disclosed concretely. As shown in Comparative Example 5 of the present specification which follows, such a terpolymer is not satisfactory for use as seal members requiring an oil resistance such as packings, gaskets, etc.
Furthermore, JP-A-7-33410 discloses that acrylic elastomers copolymerized with fumaric acid monoalkyl ester can give cross-linked products having good alkali resistance and oil resistance, where only hexamethylenediamine carbamate, N,N'-dicinnamylidene-1,6-hexanediamine and 4,4'-methylene bis(cyclohexylamine)carbamate are exemplified as a vulcanizing agent. Actually used therein is only hexamethylenediamine carbamate and the resulting cross-linked products have not better compression set characteristics. No reference is made to the metal corrosion resistance.
Furthermore, JP-A-6-99515 discloses that acrylic elastomers copolymerized with maleic acid monoalkyl ester are not satisfactory in the compression set characteristics.
Metal members, particularly iron or aluminum members are much used as automobile members. Iron members include cast irons such as FC, FCD, etc., carbon steel cast irons such as SC, etc., structural alloy steels such as SCr, SCM, SNCM, etc., heat-resisting steel such as SUH, etc. and so on. Aluminum members include alloys with a corrosion resistance-improving metal such as Cu, Si, Zn, etc., for example, alloys used mainly as high strength alloys (for structural purpose), heat-resisting alloy, etc. upon various plating treatment for corrosion resistance.
However, even these plated metal members are not satisfactory in the metal corrosion resistance yet. Plating layers may be damaged due to erosion through pinholes, cracks, etc. or due to acidic substances generated from the vulcanized rubber during the long-term service, resulting in decrease in the corrosion-preventing effect. Thus, the vulcanized rubber requires a metal corrosion resistance, and when it is used in the automobile engine room and exposed to high temperatures (about 150.degree. C.), metal corrosion may be further accelerated.
Seal members or hose members are often used in contact with both air and oil and thus are much susceptible to deterioration of rubber components due to additives, etc. presented in oil such as engine oil, AFT oil, gear oil, etc., or to oxidative deterioration at high temperatures on the air side. Thus, the molding materials must have good resistances to these two deteriorations.